A 49-year-old man has been arrested at Southend Airport on suspicion of preparation of acts to commit terrorism, the Metropolitan Police said.
Officers from the Met's Counter Terrorism Command detained the man at the Essex airport on Tuesday.
He was arrested on suspicion of preparation of acts to commit terrorism, under section 5 of the Terrorism Act 2006.
The suspect was taken to a south London police station where he remains in custody.
Officers also carried out a search at an address in Essex.